Is how you're feeling now related to that guy who rejected you? I think what you're going to have to do is, discipline yourself - put it completely out of your mind. You don't want to end up losing your job because then you'll have even bigger problems.

If this is over this guy - I think you know this has reached a bad point. You can't let what happened affect you like this. Try practicing mindfulness - every time your mind wonders, pull yourself back and focus on your job or what ever else you're doing.